As M-MTax said, if you sold the property at a gain, it is very possible that the numbers on lines 9 are very large, which could drastically increase your tax.
As far as why it only triggers when you get rid of the zero in Box 1, TurboTax isn't set up for amounts in Box 1 and 2 (you need to enter them as separate K-1s), so I'm wondering if the program isn't taking into account the amounts in Boxes 9 until you get rid of that sort-of error.
